1. Field of the Invention
The present invention relates to a memory check apparatus and method for checking abnormality of data such as leaned control values and diagnosis results stored in a memory.
2. Background of the Invention
An electronic control apparatus for vehicle engines has a backup RAM, which is continuously supplied with electric power even after an ignition switch is turned off so that various data such as engine diagnosis results and learned control values are kept stored to be used later in engine control and diagnosis.
Those data stored in the backup RAM may be broken or changed due to external electrical noises, etc. It is therefore proposed to check periodically the backup RAM and initialize the memory upon detection of abnormality of the stored data.
In one proposal, all the memory data are checked every time the ignition switch is turned on. However, this method cannot check abnormal changes of the data, which may occur after the ignition switch is turned on and the control apparatus is in engine control operation, resulting in erroneous calculation of the control quantity.
In another proposal, the memory data are checked at every specified time interval after the ignition switch is turned on (JP-A-6-250940), or within an idle period in which no calculation program is executed (JP-A-10-83355). In this method also, the control quantity may be calculated erroneously due to memory data abnormality occurring between timings of successive memory checking.